Method for producing vinyl acetate monomer from ethane or ethylene oxidation

ABSTRACT

Methods for the catalytic production of vinyl acetate monomer from ethane, ethylene or an ethanelethylene mixture using a first catalyst containing MoVNbPd, MoVLaPdbX (where X is Al, Ga, Ge or Si) or MoVNbX (where X is P, B, Hf, Te, As or mixtures thereof) in the first step of oxidation and using a conventional VAM catalyst for the second step. The method produces high yields to acetic acid and vinyl acetate without the coproduction of carbon monoxide. Furthermore, the ethylene and acetic acid produced in the first step may be utilized in the second step for VAM production.

The present invention relates to a process for the production of vinylacetate monomer according to the preamble of claims 1 and 15.

The invention relates to improved integrated methods of making vinylacetate monomers from ethane or ethylene using metal oxide catalysts.

Several publications are referenced in this application. Thesereferences describe the state of the art to which this inventionpertains.

The utilization of lower alkanes (C₁-C₄) as feed stock to produce valueadded petrochemicals is an industrially desired process. Lower alkanesare low cost and environmentally acceptable because of their lowchemical reactivity. There are only a few commercially availablechemical catalytic processes, which utilize lower alkanes as a feed,such as butane to maleic anhydride.

Vinyl acetate monomer (VAM) is a well-known industrial chemical. Theproduction of VAM from ethylene, oxygen and acetic acid usingconventional VAM catalysts is known in the art. VAM is typically used asa raw material for vinyl resins such as polyvinyl acetate. VAM waspreviously primarily manufactured from the vapor phase reaction ofethylene, acetic acid and oxygen with a zinc acetate catalyst.

More recently, VAM has been produced from the vapor-phase reaction ofethylene, acetic acid and oxygen, with a palladium catalyst. Forexample, VAM may be made from ethylene wherein the first step involvesreacting the ethylene to form acetic acid, followed by a second step ofreacting a mixture of the acetic acid and ethylene to form vinylacetate.

Numerous methods are known for the catalytic oxidation of ethylene toacetic acid. See, for example, U.S. Pat. Nos. 3,792,087 and 3,970,697.Similarly, numerous methods are known for the catalytic production ofvinyl acetate by reacting ethylene with acetic acid and oxygen in thegaseous phase. See, U.S. Pat. Nos. 3,190,912; 3,637,819; 3,650,896;4,370,492; 5,185,308; and 4,902,823.

PCT Patent Publication WO 98/05620 describes the production of aceticacid and/or vinyl acetate from ethylene (or ethane) using a firstcatalyst active for the oxidation of ethylene to acetic acid and/oractive for the oxidation of ethane to acetic acid, ethylene and carbonmonoxide, and a second catalyst active for the production of vinylacetate. The patent also describes an additional necessary step forconversion of carbon monoxide to carbon dioxide. This is because carbonmonoxide is poisonous to the VAM catalyst.

U.S. Pat. No. 4,188,490 relates to a catalytic oxidation process for theproduction of mixtures of acetic acid and vinyl acetate comprising thestep of contacting a feed mixture containing ethylene, oxygen and water(as steam) with a catalyst composition to provide a mixture of aceticacid and vinyl acetate. The catalyst system comprises a palladium metalon a zinc oxide support treated in the presence of a sulfur modifier.The method requires the subsequent step of fractional distillation toseparate the acetic acid from the vinyl acetate. Alternatively, theacetic acid contained in the product mixture is converted in situ to analkali metal salt such as sodium acetate. The method also requires thestep of treating the catalyst with the sulfur modifier by, for example,flowing moist air containing SO₂ over the catalyst at 200° C. for aboutone hour.

WO 99/13980 discloses an oxide catalyst comprising the elements Mo, Vand Nb with small amounts of phosphorus, boron, hafnium, Te and/or As.The modified catalyst provides both higher selectivity and yield ofacetic acid in the low temperature oxidation of ethane with molecularoxygen-containing gas. A process for the higher selective production ofacetic acid by the catalytic oxidation of ethane wish oxygen, in thepresence of the improved catalyst.

WO 98/05620 describes acetic acid and/or vinyl acetate which areproduced by an integrated process which comprises the steps: (a)contacting in a first reaction zone a gaseous feedstock comprisingethylene and/or ethane and optionally steam with a molecularoxygen-containing gas in the presence of a catalyst active for theoxidation of ethylene to acetic acid and/or ethane to acetic acid andethylene to produce a first product stream comprising acetic acid, waterand ethylene (either as unreacted ethylene and/or as co-producedethylene) and optionally also ethane, carbon monoxide, carbon dioxideand/or nitrogen; (b) contacting in a second reaction the presence orabsence of additional ethylene and/or acetic acid at least a portion ofthe first gaseous product stream comprising at least acetic acid andethylene and optionally also one or more of water, ethane, carbonmonoxide, carbon dioxide and/or nitrogen with a molecularoxygen-containing gas in the presence of a catalyst active for theproduction of vinyl acetate to produce a second product streamcomprising vinyl acetate, water, acetic acid and optionally ethylene;(c) separating the product stream from step (b) by distillation into anoverhead azeotrope fraction comprising vinyl acetate and water and abase fraction comprising acetic acid, (d) either (i) recovering aceticacid from the base fraction separated in step (c) and optionallyrecycling the azeotrope fraction separated in step (c) after partial orcomplete separation of the water therefrom to step (c) or (ii)recovering vinyl acetate from the azeotrope fraction separated in step(c) and optionally recycling the base fraction separated in step (c) tostep (b), or (iii) recovering acetic acid from the base fractionseparated in step (c) and recovering vinyl acetate from the overheadazeotrope fraction recovered in step (c).

DE-A-19630832 relates to a process for the selective preparation ofacetic acid from a gaseous feed comprising ethane, ethylene or mixturesthereof plus oxygen at elevated temperature, which comprises bringingthe gaseous feed into contact with a catalyst comprising the elementsMo, Pd, X and Y in gram atom ratios a:b:c:d in combination with oxygenwhere the symbols X and Y have the following meanings; X is one or moreelements selected from the group consisting of: Cr, Mn, Nb, Ta, Ti, V,Te and/or W, in particular Nb, v and W; Y is one or more elementsselected from the group consisting of: B, Al, Ga, In, Pt, Zn, Cd, Bi,Ce, Co, Cu, Rh, Ir, Au, Ag, Fe, Ru, Os, K, Rb, Co, Mg, Ca, Sr, Ba, Zr,Hf, Ni, P, Pb, Sb, Si, Sn, TI and U, in particular Ca, Sb, Te, and Li.This invention further provides a catalyst for the selective preparationof acetic acid comprising the elements Mo, Pd, X and Y in the gram atomratios a:b:c:d in combination with oxygen.

Several methods for producing vinyl acetate from ethylene result in theproduction of carbon monoxide. The production of carbon monoxide isdisadvantageous because it is poisonous to the second stage catalyst.Moreover, carbon monoxide is also a less desirable by-product due toenvironmental law constraints. In order to avoid this problem, it isnecessary to introduce another catalytic reactor for the total oxidationof CO to CO₂. This can add significant costs to the catalytic process.

Accordingly, it would be desirable to provide an improved method for theselective production of vinyl acetate monomer from ethane without theproduction of carbon monoxide.

It is an object of the invention to overcome the above-identifieddeficiencies.

It is another object of the invention to provide an improved catalyticmethod for the production of vinyl acetate.

It is a further object of the invention to provide an improved catalyticmethod for the oxidation of ethylene to produce vinyl acetate.

It is a further object of the invention to provide an improved catalyticmethod for the oxidation of ethane to produce vinyl acetate.

It is a still further object of the invention to provide an improvedcatalytic method for the oxidation of ethane, ethylene or a mixture ofethane and ethylene to produce vinyl acetate without the production ofcarbon monoxide as a by-product.

It is yet another object of the invention to provide an improvedcatalytic method for the single stage oxidation of ethane or ethylene ormixtures thereof to vinyl acetate.

The foregoing and other objects and advantages of the invention will beset forth in or be apparent from the following description.

The process of the present invention is defined in the characterizingportion of claims 1 and 15.

According to the present invention, vinyl acetate is producedcatalytically from ethane feed stocks. Another aspect of the inventionrelates to the production of vinyl acetate from ethylene. The catalystssuitable for use in the methods of the invention are active andselective to the desired end product, vinyl acetate. The catalyticprocess for the production of VAM from ethane involves two steps. In thefirst step, a catalyst (the “first catalyst”) is used to provide thefunction of activation of ethane to ethylene and acetic acid. In thesecond step, ethylene and acetic acid are further oxidized to VAM in thepresence of a conventional VAM catalyst (the “second catalyst”). Anotherpreferred embodiment relates to a method of forming a stoichiometricmixture of ethylene and acetic acid using the first catalyst, whichmixture can be directly fed into a vinyl acetate reactor containing theVAM catalyst without adjustments. Yet another preferred embodimentrelates to a catalytic method wherein ethylene or ethane is converted tovinyl acetate in a single stage reactor.

Advantageously, the preferred catalytic methods of the invention do notproduce carbon monoxide. This is advantageous because carbon monoxide isnot environmentally friendly and can have a significant impact on downstream separation costs, as well as on the poisoning of the VAMcatalyst.

Other objects as well as aspects, features and advantages of the presentinvention will become apparent from a study of the presentspecification, including the claims, figures and specific examples.

FIG. 1 is a schematical representation of a ethane to VAM reactionscheme according to one embodiment of the invention.

FIG. 2 is a schematical representation of a ethane to VAM reactionscheme according to another embodiment of the invention.

The invention relates to novel methods of producing vinyl acetate. Inthe first step, the first catalyst is used which provides the dualfunctions of (a) activation of ethane (or ethane/ethylene) to aceticacid and ethylene and (b) ethylene to acetic acid. In the second step,vinyl acetate is formed through further oxidation of ethylene withacetic acid in the presence of a second catalyst, the VAM catalyst.According to one preferred embodiment, the catalysts of the inventioncan also be used to provide an optimal feed to a vinyl acetate reactor.That is, catalytically oxidizing ethane (or ethylene/ethane) to form amixture containing the optimal stoichiometric mixture of ethylene andacetic acid for use as a feed to a vinyl acetate reactor containing theconventional VAM catalyst, such as a Pd/Al catalyst.

The catalyst system suitable for the first step of the present invention(the first catalyst) can be formed from compositions including acatalyst (a) of the formula Mo_(a)V_(b)Nb_(c)Pd_(d), wherein:

a is 1 to 5;

b is 0 to 0.5;

c is 0.01 to 0.5; and

d is >0 to 0.2.

The numerical values of a, b, c and d represent the relative gram-atomratios of the elements Mo, V, Nb and Pd, respectively, in the catalyst.The elements are preferably present in combination with oxygen in theform of various oxides.

Another catalyst system, catalyst (b), has a composition comprising theelements Mo, V, Pd, Nb, La, and X where X is Al, Ga, Si, or Ge) in theform of oxides in the ratio Mo_(a)V_(b)La_(c)Pd_(d)Nb_(e)X_(e) wherein:

a is 1;

b is 0.01 to 0.9;

c is >0 to 0.2;

d is >0 to 0.2.

e is >0 to 0.2; and

f is >0 to 0.3.

The numerical values of a, b, c, d, e and f represent the relativegram-atom ratios of the elements Mo, V, Pd, La, Nb and X, respectively,in the catalyst. The elements are preferably present in combination withoxygen in the form of various oxides.

Another catalyst system, catalyst (c), suitable for the invention isformed from a calcined composition of MO_(a)V_(b)Nb_(c)X_(d), wherein:

X is at least one promoter element selected from the group consistingof: P, B, Hf, Te, and As;

a is 1 to 5;

b is 1;

c is 0.01 to 0.5; and

d is 0 to 0.1.

The numerical values of a, b, c and d represent the relative gram-atomratios of the elements Mo, V, Nb and X, respectively, in the catalyst.The elements are preferably present in combination with oxygen in theform of various oxides.

The first catalyst (catalysts (a) or (b) or (c) or mixtures thereof) andmethods of making the first catalyst are set forth in U.S. Pat. No.6,043,597, filed Sep. 17, 1997, entitled “Catalysts for the Oxidation ofEthane to Acetic Acid, Processes of Making the Same and Processes ofUsing the Same”; U.S. Pat. No. 6,030,292, filed Dec. 24, 1997, entitled“Catalyst for Producing Acetic Acid from Ethane Oxidation, Processes ofMaking the Same and Methods of Using the Same” and U.S. Pat. No.6,060,421, filed Dec. 23, 1998, entitled “Catalysts for the Oxidation ofEthane to Acetic Acid, Methods of Making and Using the Same”.

One broad aspect of the invention relates to the production of vinylacetate from ethane, ethylene or mixtures of ethane and ethylene. Themethod utilizes a first catalyst ((a) or (b) or (c) or mixtures thereof)providing the functions of activation of ethane to acetic acid andethylene and further oxidation of ethylene with acetic acid to vinylacetate using a conventional VAM catalyst such as a Pd/Al catalyst.Overall, the recycled yield for vinyl acetate can be greater than 95%.

Advantageously, the methods of the invention produce vinyl acetate withzero (or nondetectable) or insignificant production of carbon monoxide.Preferably, less than 0.1 wt % carbon monoxide is produced as an endproduct using the invention, more preferably less than 0.01% and mostpreferred no detectable carbon monoxide is produced. Accordingly, onepreferred aspect of the invention relates to a method which employs acatalyst designed in such way that it does not produce any CO, whichsaves the treatment step of converting CO to CO₂.

One embodiment of the invention comprises reacting ethane with oxygenand water (e.g. steam) in the presence of a first catalyst ((a) or (b)or (c) or mixtures thereof) to form a mixture containing ethylene andacetic acid which is then reacted to form vinyl acetate.

The raw material used as the source for the ethane or ethylene/ethanecan be a gas stream, which preferably contains at least five volumepercent of ethane/ethylene. The gas can also contain minor amounts ofthe C₃-C₄ alkanes and alkenes, preferably less than five volume percentof each. The gas stream can also contain major amounts, preferably morethan five volume percent, of nitrogen, carbon dioxide, and water in theform of steam.

The reaction mixture useful in carrying out the process is generallyfrom 5 to 50 moles % of ethane, 5 to 50 moles % of molecular oxygeneither as pure oxygen or in the form of air, and optionally 2 to 50moles t of water in the form of steam. The amount of oxygen present maybe a stoichiometric amount, or lower, of the hydrocarbons in the feed.Other gases may be used as reaction diluents or heat moderators such ashelium, nitrogen, and carbon dioxide.

The gaseous components of the reaction mixture are preferably uniformlyadmixed prior to being introduced into the reaction zone. The componentsmay be preheated, individually or after being mixed, prior to beingintroduced into the reaction zone.

The first reaction zone, containing the first catalyst ((a) Pr (b) or(c) or mixtures thereof), generally has a pressure of from 1 to 34 bar(15 to 500 psi), preferably from 10 to 24 bar (150 to 350 psi); atemperature of from about 100° C. to about 450° C. preferably from 200°C. to 350° C. more preferably from 250° C. to 300° C.; a contact timebetween the reaction mixture and the catalyst of from about 2 seconds toabout 100 seconds, preferably from 5 seconds to 30 seconds; and a spacehourly velocity of from about 50 to about 50,000 h⁻¹, preferably from100 to 10,000 h⁻¹ and most preferably from 200 to 3,000 h⁻¹.

According to one preferred embodiment, the process occurs in two stages.In the first stage, a mixture comprising ethane or ethylene, oxygen or acompound capable of providing oxygen and water (e.g., steam) is reactedto form a mixture containing ethylene, acetic acid, oxygen and water(e.g., steam). The product mixture of the first stage is then fed intothe second stage and reacted to produce vinyl acetate.

The feed from the first stage may be adjusted prior to being introducedinto the second stage. For example, the oxygen, ethylene and acetic acidconcentration may be adjusted to optimize the catalytic reaction.Preferably, the first stage of the process produces a stoichiometriccomposition of acetic acid and ethylene as a feed for the second stage.According to one particularly preferred embodiment, adjustments of thefeed for the second reactor are not required as the mixture produced inthe first stage can be directly fed into the second stage. Thus, adual-function catalyst can be used in the first stage to provide thefeed stock for the second stage, which may contain a conventional Pd/AlVAM catalyst or any catalyst suitable for converting the feed stock ofacetic acid and ethylene to VAM.

Therefore, using the present invention, VAM can also be directlyproduced from only ethane, oxygen and water without additionalcomponents since the outlet of the first reactor may be optimized tocontain a stoichiometric mixture of acetic acid, ethylene and oxygenwhich is the feed mixture for the second reactor. Preferably, thetemperature and pressure of the feed from the first stage are also notadjusted prior to the second stage.

According to one embodiment, the output from either the first or secondstage is recycled into the same or an earlier stage. For example, theoutput from stage 1 may be recycled into stage 1 or the output fromstage 2 may be recycled into stage 1 and/or stage 2.

According to another embodiment, the reaction zone comprises multiplestages of bilayered catalyst consisting of layers of a first catalyst((a) or (b) or (c) or mixtures thereof) according to the invention and asecond conventional vinyl acetate catalyst. In this manner, the firstcatalyst converts ethane to a mixture of acetic acid and ethylene,preferably to an optimal mixture, and the second catalyst converts theethylene/acetic acid to vinyl acetate in a single reaction zone.

Accordingly, one preferred embodiment relates to a process carried outin a single stage with all the reactants being supplied as a single feedwith unreacted initial reactants being recycled. However, multiple stageaddition of oxygen to the reactor with an intermediate hydrocarbon feedcan also be used. This may improve productivity to vinyl acetate andavoid potentially hazardous conditions.

Two possible integrated schemes using the first catalyst and the secondVAM catalyst for direct production of VAM from ethane or ethane/ethylenemixtures without producing carbon monoxide are shown in FIGS. 1 and 2.

FIG. 1 is schematical representation of one reaction scheme A accordingto one embodiment of the invention. The partial oxidation reactor 1containing the first catalyst (CAT-A) converts fresh and recycled ethaneor ethane/ethylene with oxygen into ethylene, acetic acid and carbondioxide. An optimum amount of water from distillation reactor 3 is alsointroduced to partial oxidation reactor 1 in order to increase theacetic acid selectivity. The effluent from partial oxidation reactor 1enters a gas/liquid separation unit 2. The gas stream from gas/liquidseparation unit 2 is recycled to partial oxidation reactor 1 or goes tocarbon dioxide absorption unit 4, where CO₂ is removed. The liquidstream from gas/liquid separation unit 2 goes to distillation unit 3,where acetic acid is separated from water or the liquid stream fromgas/liquid separation unit 2 can directly go to VAM reactor 5 containinga conventional VAM catalyst (CAT-B). The treated gases consisting ofethane, ethylene and oxygen and the liquid stream consisting of aceticacid or acetic acid and water are fed to VAM reactor 5 to produce VAM,CO₂ and unreacted ethane, ethylene and acetic acid. The effluent of VAMreactor 5 is then fed to gas liquid separation unit 6 where gasesincluding ethane, ethylene and CO₂ are separated, partially purged tocontrol the build up of non reacting species in purge unit 8 andrecycled back to partial oxidation reactor 1. The liquids are sent todistillation unit 7 for recovery of VAM. Acetic acid or unreacted aceticacid is recycled back to VAM reactor 5.

FIG. 2 is a schematical representation of reaction scheme B according toanother embodiment of the invention. The partial oxidation reactor 21containing the first catalyst (CAT-A) converts fresh and recycled ethaneor ethane/ethylene with oxygen into ethylene, acetic acid and carbondioxide. The effluent of reactor 21 is fed to VAM reactor 23 containingthe VAM catalyst (CAT-B) via optional heat exchanger 22, which allowsadjustment of the temperature of the feed to VAM reactor 23. Optionally,the two catalysts CAT-A and CAT-B can be in one reactor in the form of aphysical mixture or in alternating layer form. Additional amounts ofgases to VAM reactor 23, such as ethylene, acetic acid, and oxygen maybe added depending upon the process conditions. The effluent from VAMreactor 23 is fed to gas/liquid separation unit 24, where gasesincluding CO₂, C₂H₄, and C₂H₆, are separated from liquid VAM, aceticacid and water. The gas streams from gas/liquid separation unit 24 arerecycled via carbon dioxide removal unit 25 to reactor 21. Optionally,the gas streams can also be recycled to reactor 21 without theabsorption unit 25, as the catalyst CAT-A in the reactor 21 is notaffected by the presence of carbon dioxide. Further, a specific amountof carbon dioxide also enhances the performance of the catalyst CAT-A.Gases are partially purged to control the build of non reacting speciesin purge unit 27. Liquid stream from separator unit 24 is fed todistillation unit 26 where acetic acid is separated from VAM and waterand is optionally recycled to reactor 23 for make up or can berecovered. VAM goes to a recovery unit and H₂O is recycled to reactorunit 21 for enhancement of acetic acid and selectivity.

EXAMPLES

Catalytic oxidation processes using a first catalyst ((a) or (b) or (c)or mixtures thereof) were carried out in a tubular reactor under thefollowing conditions. All experiments were run at the temperatures setforth below ranging from 260° C. to 286° C., at a pressure of about 14bar (200 psig)

Reaction products were analyzed on-line by gas chromatography. Oxygen,nitrogen and carbon monoxide were analyzed using a 3 mm by 3 mm columnof 13×molecular sieve. Carbon dioxide, ethane, ethylene and water wereanalyzed using a 1.8 m by 3 mm column packed with material sold underthe name HAYASEP™Q. Acetic acid was analyzed using a 0.5 m by 3 mmcolumn packed with material sold under the name PORAPACK™ N.

In all cases, the conversion and selectivity calculations were based onthe stoichiometry.

Data for the stage I reaction mentioned in the examples is experimentaland the production of vinyl acetate (VAM) data in the stage II iscalculated based on 92% yield to VAM from ethylene (Chem. System 91-10,October 1992).

Example 1

The production of Van from Ethylene:

The first catalyst (catalyst (a)): MoV_(0.396)Nb_(0.128)Pd_(x)O_(y)(where x=1.90e-04and y is based on the co-ordination valence).

Process conditions for stage I reactor: 286° C./14 bar (200 psi).

Process conditions for stage II reactor as described in reference Chem.System 91-10, October 1992.

Results Data:

Compound Stage I Stage II (g. mol. min.) Feed Product Feed ProductEthylene 5.65E−4 2.07E−4 2.07E−4 Oxygen 6.73E−4 1.23E−4 1.23E−4 Nitrogen2.53E−3 2.47E−4 Water 2.23E−5 2.13E−4 Acetic Acid 2.80E−4 2.80E−4 CO₂1.56E−4 VAM 1.90E−4

The nitrogen, CO₂ and water are diluents in the stage II reaction.

Example 2

The Production of VAN from Ethane

First catalyst (catalyst (a)): MoV_(0.396)Nb_(0.128)Pd_(x)O_(y) (where xis 1.90e-04 and y is based on the co-ordination valence).

Process conditions for stage I reactor: 286° C./14 bar (200 psi).

Process conditions for stage II reactor as described in Chem. System91-10, October 1992.

Results Data:

Compound Stage I Stage II (g. mol. min.) Feed Product Feed ProductEthane 4.43E−04 2.40E−4  Oxygen 5.10E−04 5.07E−05 5.07E−05 Nitrogen1.92E−03 1.98E−03 Water 3.18E−04 Ethylene 8.86E−05 8.86E−05 Acetic Acid9.28E−05 9.28E−05 CO₂ 1.77E−04 VAM 9.00E−5

The nitrogen, CO₂ and water act as diluents in stage II.

Example 3

The Production of VAX from Ethane

First catalyst (catalyst (a)): Mo_(2.5)V_(1.0)Nb_(0.32)Pd_(0.03)O_(y)(where y is based on the coordination valence).

Process conditions for stage I reactor: 286° C./14 bar (200 psi) Processconditions for stage II reactor as described in chem. Systm 91-10,October 1992.

Results Data:

Compound Stage I Stage II (g. mol. min.) Feed Product Feed ProductEthane 1.91E−04 7.87E−05 Oxygen 2.25E−04 1.30E−05 5.07E-5 Nitrogen8.45E−04 8.40E−04 Water 1.87E−04 Ethylene 3.41E−05 3.41E−05 Acetic Acid4.08E−05 4.08E−05 CO₂ 3.53E−05 CO 4.68E−05 VAM 3.13E−5

The nitrogen, CO₂ and water act as diluents in stage II.

Based on the above-described catalytic data, the following generalcharacteristics can be concluded for the methods of the invention:

1. The catalytic methods used show high selectivity to vinyl acetate byoxidizing mixtures of ethane and ethylene.

2. The catalytic methods used also show high selectivity to vinylacetate by oxidizing ethane.

3. The catalytic method systems used produce vinyl acetate without theproduction of by-products such as carbon monoxide. This advantagereduces the step of CO conversion to CO₂ in the conventional VAMprocess.

What is claimed is:
 1. A process for the production of vinyl acetatemonomer comprising the steps of: (1) contacting a gaseous feed mixtureof ethane or ethylene or ethane/ethylene, steam and a molecular oxygencontaining gas in the presence of a first catalyst active for oxidationof ethane, ethylene or ethane/ethylene to produce a selective stream ofacetic acid, ethylene, carbon dioxide and water and (2) converting asecond feed mixture comprising ethylene, acetic acid and oxygen to vinylacetate monomer in the presence of a second catalyst active for theproduction of vinyl acetate, wherein said process does not include anintermediate separation step to remove the CO between the two reactionsteps characterized by using a first oxidation catalyst selected fromthe following catalyst compositions: a catalyst composition comprisingthe elements Mo, V, Nb, and Pd, in the form of oxides, in the ratioMo_(a)V_(b)Nb_(c)Pd_(d) wherein: a is 1 to 5; b is 0 to 0.5; c is 0.01to 0.5; and d is >0 to 0.2; a, b, c, d, represent the relative gram-atomratios of the elements Mo, V, Nb, and Pd respectively in the catalyst ora catalyst composition comprising the elements Mo, V, Pd, Nb, La and X,in the form of oxides, wherein X is Al, Ga, Si or Ge, in the ratioMo_(a)V_(b)La_(c)Pd_(d)Nb_(e)X_(f), wherein: a is 1; b is 0.01 to 0.9; cis >0 to 0.2; d is >0 to 0.2; e is >0 to 0.2; f is >0 to 0.3; a, b, c,d, e, f represent the relative gram-atom ratios of the elements Mo, V,La, Pd, Nb, and X respectively in the catalyst or a catalyst compositioncomprising the elements Mo, V, Nb and X (where X is P, B, Hf, Te, As ormixtures thereof) in the form of an oxide, in the following ratioMo_(a)V_(b)Nb_(c)X_(d) wherein: a is 1 to 5; b is >0 to 0.1; c is 0.01to 0.5; d is >0 to 0.1; a, b, c, d represent the relative gram-atomratios of the elements Mo, V, Nb, and X respectively in the catalyst ora mixture between the two previous first oxidation catalysts and acatalyst composition comprising the elements Mo, V, Nb, and Pd, in theform of oxides, in the ratio Mo_(a)V_(b)Nb_(c)Pd_(d) wherein: a is 1 to5; b is 0 to 0.5; c is 0.01 to 0.5; and d is >0 to 0.2; a, b, c, drepresent the relative gram-atom ratios of the elements Mo, V, Nb, andPd respectively in the catalyst.
 2. The process of claim 1, wherein saidprocess produces no carbon monoxide.
 3. The process of claim 2, whereinsaid first catalyst and second catalyst are in the form of a fixed orfluidized bed or a solid moving bed reactor.
 4. The process of claim 2,wherein said feed mixture is fed into a second reaction zone.
 5. Theprocess of claim 4, wherein the second feed mixture for the second stepcomprises ethylene, acetic acid, CO₂ and oxygen.
 6. The process of claim2, wherein said feed mixture comprises molecular oxygen ranging from 0.1to 25% by volume of the feed mixture.
 7. The process of claim 2, whereinsaid feed mixture is diluted with N₂ in an amount ranging from 5 to 90%by volume.
 8. The process of claim 2, wherein said feed mixture isdiluted with steam in an amount ranging from 0 to 40% by volume.
 9. Theprocess of claim 2, wherein said feed mixture comprises from 1% to 95%by volume of ethane, ethylene or mixtures thereof.
 10. The process ofclaim 2, wherein first step oxidation is achieved at a temperature offrom 150 to 450° C., under a pressure of from 1 to 34 bar (15 to 500psi), and with a contact time between reaction mixture and the catalystof from 2 to 100 seconds.
 11. The process of claim 2, wherein saidcontacting comprises reacting ethane/ethylene with steam and oxygen or acompound capable of providing oxygen in the presence of said firstcatalyst in a first reaction zone to form a first product mixturecomprising ethylene, oxygen, steam and acetic acid and.the said firstproduct mixture is fed into a second reaction zone wherein the ethyleneand acetic acid react to form vinyl acetate in the presence of saidsecond reaction catalyst.
 12. The process of claim 11, wherein saidfirst product mixture is fed directly into said second reaction zonewithout adding additional components.
 13. The process of claim 11,wherein said first product mixture is fed into said second reaction zonewith addition/adjustment of ethylene, acetic acid, oxygen orcombinations thereof.
 14. The process of claim 11, wherein said firstproduct mixture is subjected to temperature and/or pressure adjustmentsprior to being fed into said second reaction zone.
 15. A process ofproducing vinyl acetate monomer comprising the step of catalyticallyoxidizing ethane to form vinyl acetate in a single reaction zonecontaining a first catalyst having activity for oxidation or ethane toethylene and acetic acid and a second catalyst having activity foroxidation of ethylene with acetic acid to vinyl acetate, characterizedin that said first catalyst is at least one catalyst selected from thefollowing catalyst compositions: a catalyst composition comprising theelements Mo, V, Pd, Nb, La and X, in the form of oxides, wherein X isAl, Ga, Si or Ge, in the ratio MO_(a).V_(b) La_(c), Pd_(d)Nb_(e)X_(f),wherein: a is 1; b is 0.01 to 0.9; c is >0 to 0.2; d is >0 to 0.2; eis >0 to 0.2; f is >0 to 0.3; a, b, c, d, e, f represent the relativegram-atom ratios of the elements Mo, V, La, Pd, Nb, and X respectivelyin the catalyst or a catalyst composition comprising the elements Mo, V,Nb and X (where X is P, B, Hf, Te, As or mixtures thereof) in the formof an oxide, in the following ratio MO_(a)V_(b)Nb_(c)X_(d) wherein: a is1 to 5; b is >0 to 0.1; c is 0.01 to 0.5; d is 0 to 0.1; a, b, c, drepresent the relative gram-atom ratios of the elements Mo, V, Nb, and Xrespectively in the catalyst or a mixture between the two previous firstoxidation catalysts and a catalyst composition comprising the elementsMo, V, Nb, and Pd, in the form of oxides, in the ratioMo_(a).V_(b)Nb_(c)Pd_(d) wherein: a is 1 to 5; b is 0 to 0.5; c is 0.01to 0.5; and d is >0 to 0.2; a, b, c, d represent the relative gram-atomratios of the elements Mo, V, Nb, and Pd respectively in the catalyst.